1. Field of the Invention
The present invention relates to a navigation assisting apparatus to be mounted in an aircraft, an aircraft in which the navigation assisting apparatus is mounted, a navigation assisting method and a navigation assist processing program recorded in a storage medium. In particular, the present invention relates to a four-dimensional navigation method. The four-dimensional navigation method deals with navigation including management on the basis of time in addition to three-dimensional navigation which manages the status of an aircraft on the basis of Latitude, Longitude and altitude.
2. Description of the Related Art
A conventional navigation assisting apparatus is ready for three-dimensional navigation, which manages the status of an aircraft on the basis of Latitude, Longitude and altitude. Three-dimensional navigation manages the positional accuracy of an aircraft and the distance between aircrafts. To manage aircraft navigation accuracy, concepts of RNP (Required Navigation Performance), ANP (Actual Navigation Performance), etc., are used.
An FMC (Flight Management Computer) mounted in an aircraft calculates ANP on the basis of data supplied from a plurality of navigation sensors. The ANP values are monitored by the FMC itself or a pilot using an MCDU (Multi-functional Control Display Unit) so as not to exceed the range defined by RNP.
The altitude of an aircraft is acquired by a GPS receiver, a radio altimeter or a barometric altimeter. Whether the aircraft maintains a target altitude or not is monitored by the pilot or the FMC itself. The position of the aircraft in the along track (the direction in which the aircraft travels) is managed with reference to time such that, for example, an interval of at least two minutes is kept between the aircraft and the preceding one. Thus, according to conventional navigation, the position of an aircraft is managed three-dimensionally.
In recent years, air transportation has been tightly scheduled to meet economic demands in particular. It is certain that CNS/ATM (Communication Navigation Surveillance/Air Traffic Management) will be introduced into air traffic management in future. Introduction of CNS/ATM will further tighten air transportation schedules.
Conventionally, however, flight intervals are managed with a large time margin to assure safety. This is disadvantageous in increasing the efficiency of air transportation.
Under the circumstances, four-dimensional navigation, which includes a time management factor in addition to the factors of three-dimensional navigation, has been proposed as a new concept of air traffic control. Under the proposal, recent FMCs have been equipped with an RTA (Required Time of Arrival) function. If air traffic control comes to include time management, the time margin can be minimized, so that an economical air service can be expected.
Thus, in recent years, it is a social requirement to offer an economical air service while maintaining a high level of safety. Because of these circumstances, the function for controlling time in management of aircraft has been reinforced. An important problem to be solved in air service is to optimally set the flight interval of aircraft along the track by time management.